First, a method for producing a single crystal by using the Czochralski method will be described. In FIG. 3, a schematic sectional view of a conventional single crystal production apparatus is depicted.
A single crystal production apparatus 101 depicted in FIG. 3 includes a main chamber 109a in which a crucible 102 containing raw material melt 104, which is a raw material of a single crystal, is disposed and a pull chamber 109b that is connected to the main chamber 109a, for holding the single crystal 105 pulled from the raw material melt 104 and taking out a single crystal 105.
Near the center of the interior of the main chamber 109a, the crucible 102 containing the raw material melt 104 is disposed. The raw material is melted by causing a heater 103 provided around the crucible 102 to generate heat and the resultant high-temperature raw material melt 104 is held in the crucible 102. Moreover, around the perimeter of the heater 103, a heat insulating cylinder 107 is provided to prevent the heat generated by the heater from escaping and protect the main chamber 109a. 
When a seed crystal 108 for the single crystal 105 which is grown while being pulled by a pulling shaft 106 is a silicon single crystal, the crucible that directly holds the raw material melt 104 is a quartz crucible 102a, and, since this quartz crucible 102a is softened at a high temperature and is brittle and fragile, the exterior of the quartz crucible 102a is supported by a graphite crucible 102b. 
In addition, in the growth of a single crystal by using the Czochralski method, since the crystal is grown with the crucible 102 and the seed crystal 108 being rotated in opposite directions, a pedestal 110 for supporting the crucible 102 and a crucible rotating shaft 111 for rotating the crucible 102 via the pedestal 110 are attached to a lower part of the graphite crucible 102b. 
When a single crystal is produced by using such an apparatus, the following problem arises. The high-temperature raw material melt held in the crucible may flow to the outside of the crucible in an unexpected accident or the like and erode and degrade the crucible rotating shaft, a crucible drive, cooling-water piping, and the like (hereinafter also referred to as metal portions) that are generally disposed below the pedestal and have an exposed metal surface. In particular, when the cooling-water piping is eroded, the apparatus suffers damage, which may result in creating a risk of an accident.
Therefore, in case the crucible holding the raw material melt gets broken and the melt leaks into a furnace, various melt-leak-preventing structures in the production apparatus have been developed.
For example, in an area below the crucible 102 containing the raw material melt 104, a melt draining means (not shown) such as a melt-draining groove, a fin, a flange, and the like is provided, and, in the bottom of the main chamber 109a, a graphite melt receiver 113 provided with a center sleeve 112 is provided (See Patent Document 1). With such a structure, even when a crack appears in the crucible and the melt flows out through the crack, the melt draining unit makes the melt drop into the melt receiver 113 in the bottom of the main chamber 109a, and the melt is stored in the melt receiver 113, whereby the erosion of the metal portions below the pedestal by the high-temperature melt is suppressed.
Moreover, there is a structure in which a receiver (not shown) through which the shaft of the pedestal 110 slidably penetrates is provided at an arbitrary height of the pedestal 110 and the melt leaking from the crucible 102 is received by this receiver (See Patent Document 2).